Antenna for broadcasting two signals



July 23, 1957 D. w. PETERSON 2,800,656

ANTENNA FOR BROADCASTING TWO SIGNALS' Filed Feb. 25, 1954 2 Sheets-Sheet l 1N! TNTOR.

y 1957 D. w. PETERSON ANTENNA FOR BROADCASTING TWO SIGNALS 2 Sheets-Sheet 2 Filed Feb. 25, 1954 fig/34V rep/vs M N W mfi a mi W m M w.

United States PatentO ANTENNA FOR BROADCASTING TWO SIGNALS Donald W. Peterson, Princeton, N. l, assignor to Radio Corporation of America, a corporation of Delaware Application February 25, 1954, Serial No. 412,444

6 Claims. (Cl. 343-425) This invention relates to broadcast antennas, and more particularly to antennas for simultaneously broadcasting two signals of diflerentfrequencies.

In most communities there are relatively few advantageous sites for television broadcasting antennas. It is often desirable to mount all television antennas serving a community at the top of a single building or tower. It is especially desirable that all television antennas serving a community be located at or near the same point so that all of the directional receiving antennas may be pointed toward the one point to receive all broadcasts. For these and other economic reasons it is desirable tointerlace two antenna arrays in the same vertical aperture to simultaneously broadcast two television signals of different frequencies.

It is a general object of this invention to provide :an improved antenna construction whereby two television signals of different frequencies may be simultaneously broadcast.

It is another object to provide two improved interlaced antenna arrays operating at widely separated frequencies and both mounted on a single tower to provide omni-directional patterns in the horizontal plane.

It is a further object to provide improved omni-directional antenna arrays in a single vertical aperture, the construction being characterized by simplicity of manufacture, each of tuning, and low wind resistance.

In one aspect, the invention comprises a hollow pipe or vertical waveguide provided with a plurality of slots by which radio frequency energy supplied to the interior of the waveguide is coupled to free space. The slotted waveguide is used to broadcast a relatively high frequency television signal. A plurality of layers of four radiating elements are mounted to extend normally outward from the waveguide, each of the elements being disposed at right angles with adjacent elements. The antenna array constituted by the layers of radiator elements are fed with a television signal of relatively low frequency to broadcast a second television signal.

These and other objects and aspects of the invention will be apparent to those skilled in the art from the following more detailed description taken in conjunction with the appended drawings, wherein:

Figure 1 is a plan view of a two-signal antenna array constructed according to the teachings of this invention;

Figure 2 is an elevation of a portion of the antenna of Figure 1; and

Figure 3 is a perspective view of the antenna of Figures 1 and 2 illustrating a method of feeding the two sets of radiating elements.

Referring to the drawings, a generally circular waveguide or pipe is provided with a plurality of layers of slots, one layer having slots 11, 12, 13 and 14 spaced at 90 degrees around the pipe 10. Four similar layers of slots are shown in Figure 2. Any suitable number of layers may be employed. The slots in the pipe 10 are fed from a relatively high frequency television transmitter thru a coupling in the interior of the pipe in any one of the number of known ways to cause an omni-directional radiation pattern in the horizontal plane. The arrangement for feeding the slots may, for example, be as shown in U. S. Patent No. 2,658,143, issued on Nov. 3, 1953, to O. O. Fiet et aL, and assigned to the assignee of this application.

A plurality of layers of four external radiator elements are mounted to extend radially outward from the pipe 10, each radiator element being arranged at degrees with adjacent elements. One layer has radiator elements 15, 16, 17 and 18. Two similar layers are shown in Figure 2. Any suitable number of layers may be employed. The radiator elements 15 thru 18 have a length in the order of a quarter-wavelength at a second relatively lower frequency. The radiator elements are fed in a quadrature phase manner externally of the waveguide to operate as a turnstile antenna. The construction of the antenna ele ments, and the manner of feeding them, may be, for example, as shown and described in U. S. Patent No. 2,086,976, issued on July 13, 1937, to H. G. Brown, or U. S. Patent No. 2,267,550 issued toG. H. Brown on Dec. 23, 1941, both patents being assigned to the assignee of this application.

Fig. 3 illustrates methods by which the radiating slots and the radiating elements may be excited from a high frequency transmitter and a low frequency transmitter, respectively. 'The output of a high frequency transmitter 20 is applied thru a coaxial line 21, 22 extending into the hollow pipe 10. The inner conductor 22 is connected to a conductor 23 extending coaxially thru the hollow pipe 10. Energy applied thru the coaxial line 21, 22 excites a coaxial line mode in the coaxial line constituted by hollow pipe 10 and conductor 23. Each of the radiating 'slots in the hollow pipe 10 is provided with an in wardly extending probe designated 24 which couples energy from the coaxial line 10, 23 to the respective radiating slots from which the energy is radiated into space.

A low frequency transmitter 26 has a coaxial line output 27 which is divided into four branches. As indicated in the drawing, the branches have lengths equal to The four branches are connected respectively to the four radiating elements 15 thru 18 to excite the elements in phase-quadrature for operation as a turnstile antenna. It will be understood that the specific means shown in Figure 3 for exciting the radiating slots and the radiating elements are illustrative and that other methods may be employed.

The antenna construction of this invention is useful for simultaneously transmitting two signals of different frequency when the two frequencies difier by the ratio of at least two-to-one. In other words, the energy radiated from the slots should be at least twice as high in frequency as the energy radiated by the radiator elements. The diameter of the pipe 10 should be in the order of 0.4 wavelength at the relatively higher frequency which is radiated from the slots. The diameter of the pipe 10 cannot be a great deal in excess of 0.4 wavelength if a substantially uniform radiation pattern is to be had in all directions in the horizontal plane. The maximum diameter of the pipe 10 is therefore determined by the relatively higher frequency signal radiated from the slots. The minimum diameter for pipe 10 is determined by the requirement for sufiicient structural strength to provide a self-supporting structure.

If the relatively lower frequency to be transmitted by the radiator elements 15 thru 18 has a frequency of not more than one-half the frequency of the signal transmitted by the slots, the diameter of the pipe 10 in terms of the wavelength of the lower frequency signal is sulfiobtained at the lower frequency.

By way of example, the slotted pipe may be designed for operation at a frequency of 207 megacycles (channel 12 in the U. S.). In this case, the diameter of the pipe 10 providing a horizontal pattern of circularity of plus or minus 0.5 db would be 0.4 wavelength at 207 megacycles. designed for operation at 69 megacycles (channel 4 in the U. S.), the diameter of the pipe 10 is equal to 0.133 wavelength at the frequency of 69 megacycles. This diameter is small enough compared with the wavelength of the 69 megacycle signal so that a uniform radiation pattern is obtained in the horizontal plane for the 69 megacycle signal. At the same time, the diameter of the pipe 10 is suflicient to provide the needed structural stiffness for supporting the entire antenna array.

It is apparent that according to the construction taught by this invention that two television signals may be simultaneously broadcast from a single aperture when the frequencies of the two signals bear the ratio of at least twoto-one. By this invention, the scarce vertical space suitable for broadcasting is economically shared by two television boadcasting services.

What is claimed is:

1. An antenna array for simultaneously broadcasting a signal of relatively high frequency and a signal of relatively low frequency comprising, a pipe adapted to be mounted vertically and having a plurality of layers of slots therein, means to feed said slots with the energy at said relatively high frequency, a plurality of layers of four radiator elements extending at right angles from said pipe, each of said radiator elements being arranged at right angles with adjacent radiator elements, and means to feed said relatively low frequency signal to said radiator elements in quadrature phase relationship.

2. An antenna construction for simultaneously radiating a relatively high and low frequency signals compris- V If the radiator elements 15 thru 18 are e ing, a hollow pipe having a longitudinal aperture provided with layers of four slots in each layer, said slots being spaced degrees around said pipe, means to feed said relatively high frequency signal to said slots, a plurality of layers of four radiator elements extending from and supported by said pipe within the length of and elfective over said longitudinal aperture, said radiator elements extending at right angles with said pipe, each of said elements being spaced 90 degrees from the adjacent element, and means to turnstile feed said radiator elements.

3. An antenna construction as defined in claim 2, wherein said high frequency signal has a frequency at least twice said lower frequency signal.

4. An antenna comprising a hollow pipe having radiating slots along the length thereof and defining an aperture, means for supplying signal energy to the interior of said pipe to energize said slots, radiator elements supported by and projecting from said'pipe along the length thereof over at least a portion of said aperture, and means for feeding said radiator elements with a signal of a frequency different from the frequency of the signal energy supplied to said pipe.

5. An antenna as defined in claim 4, wherein a plurality of slots appear circumferentially on said pipe, and a plurality of radiator elements extend from said pipe at points between said slots.

6. An antenna as defined in claim 5 wherein the feed means for said radiator elements is external of said pipe.

References Cited in the file of this patent UNITED STATES PATENTS 2,267,550 Brown Dec. 23, 1941 2,479,227 Gilbert Aug. 16, 1949 2,510,290 Masters June 6, 1950 2,658,143 Fiet et a1 Nov. 3, 1953 

